At present, air vehicles that have seafaring capability only use the water as a landing platform. They have limited utility as seagoing vessels and generally only carry propulsion that is capable of efficient use during flight. Thus vehicles such as helicopters and seaplanes can only fly out and hover over points over the water for very limited durations or can land in the water but only operate in a very limited range/manner while at sea.
There are two types of seaplanes: the floatplane and the flying boat. A floatplane has pontoons mounted under the fuselage. Only the “floats” of a floatplane normally come into contact with water. The fuselage remains above water. Some small land aircraft can be modified to become float planes. In a flying boat, the main source of buoyancy is the fuselage, which acts much like a ship's hull in the water. Most flying boats have small floats mounted on their wings to keep them stable. These amphibious aircraft can often take off and land both on conventional runways and water. A true seaplane can only take off and land on water. Similarly helicopters may use floats or their hull to provide buoyancy. These helicopters like seaplanes can only take off and land on water.
Seaplanes can only take off and land on water with little or no wave action and, like other aircraft, have trouble in extreme weather. The size of waves a given design can withstand depends on, among other factors, the aircraft's size, hull or float design, and its weight. Flying boats can typically handle rougher water and are generally more stable than floatplanes while on the water.
In either case, these amphibious aircraft rely on propulsion systems best suited to flight. This propulsion system provides only limited functionality on the water's surface. For example, the vehicle may be limited to merely taxiing on the water's surface since the propulsion system typically provided operates efficiently as an aircraft and not as a seafaring vehicle. Typical single propulsion systems limit the ability of the vehicle to perform a number of duties such as, but not limited to, search and rescue, surveillance and law enforcement.